1. Field of the Invention
The present invention relates to a digital image forming apparatus in which an image of an original document is formed on a surface of a photoconductor by converting optically read image information of the original document into an analog electrical signal carrying the image information, converting the analog electrical signal to a digital signal carrying the image information and exposing the surface of the photoconductor with a laser beam modulated in accordance with the digital signal carrying the image information. More particularly the invention relates to a digital image forming apparatus capable of storing image data of an original document in a memory and changing a magnification ratio for the image according to the image data stored in the memory.
2. Discussion of the Background
In a digital image forming apparatus, an image of an original document, which is placed on a contact glass with the surface carrying the image facing downward, is read with an image reading device by illuminating the original document with a light source and imaging a light, which is reflected from the original document and which carries image information of the original document, on an image sensor as the image reading device by way of a lens system. The image sensor converts the received light carrying the image information into an analog electrical signal carrying the image information, which is then converted to a digital signal carrying the image information. Various image processing operations are then applied to the digital signal, for example, for enhancing the quality and changing the size of the outputting image.
A laser beam is modulated according to the digital signal carrying the image information end a latent image for the image information is formed on a surface of a photoconductor by the modulated laser beam. The latent image is then developed with toner to form a visible toner image. The toner image is transferred onto a sheet, which is conveyed from a sheet feeding device of the apparatus, to thereby form the image of the original document on the sheet.
A digital image forming apparatus as described above generally has a memory to store image data of an original document, which is obtained by reading the original document with an image reading device. An image of the original document is formed by reading out the image data of the original document from the memory. The digital image forming apparatus having such a memory to store image data of an original document can form, therefore, the image of an original document on a plurality of sheets, without repeatedly reading the original document in order to form the image on each of the plurality of sheets.
Further, when outputting a plurality of sets of a plurality of original documents with such a digital image forming apparatus, it is desired that each outputted set of the plurality of original documents is stacked and sorted on an exit tray such that the user can easily separate each outputted set of the original documents from other sets. Therefore, image data is generally rotated 90 degrees or 270 degrees such that the image is formed as rotated for each set of the plurality of original documents and thereby each produced set of the plurality of original documents is stacked on the exit tray one after another being alternately directed sideways and lengthways, thus enabling the easy separation of each outputted set from others on the exit tray.
When an image of an original document is read by such a digital image forming apparatus as described above, the image generally is not read in exactly the same size as the original image due to, for example, the optical characteristics of the apparatus. Therefore, when the image is formed, after being enlarged or reduced, according to the image data stored in the memory device, the size of the outputted image may further differ from the original size by, for example, 1%.
Japanese Patent Laid-open Publication No. 9-130582 describes an example of such a digital image forming apparatus having a memory to store therein image data of an original document, which is obtained by reading the original document by an image reading device. The Publication describes a technology to prevent generating a difference between the magnification ratios for the vertical and lateral directions of the image when the image is rotated 90 degree or 270 degree.
In addition, there is a need to output a plurality of images of an original document with slightly changing the magnification ratio for each of the plurality of images, such as for example, changing the magnification ratio for the image in a step of 1%. Particularly, when the original document is large, such as for example, an A0 size, there is a particular need to output a plurality of images of the original document while changing the magnification to avoid reading the original document each time when outputting an image with a different magnification. This factor is significant because the large sized document is not easy to place on a contact glass of an image forming apparatus.
In order to overcome the above-described and other problems with background apparatus and to meet the above-described need, preferred embodiments of the present invention provide a digital image forming apparatus and method which are capable of storing image data of an original document in a memory and changing the magnification ratio for the image according to the image data stored in the memory.
According to a preferred embodiment of the present invention, an image forming apparatus includes a photoconductor and an image reading device to receive and read a light reflected from an original document carrying image data of an image of the original document and to convert the received light carrying the image data into an analog electrical signal carrying the image data. An analog-to-digital converter converts the analog electrical signal carrying the image data into a digital signal carrying the digital image data and a memory to store the digital image data. An image writing device forms an image according to the digital image data on a surface of the photoconductor with a laser beam modulated according to the digital image data. According to the present invention, the image forming apparatus includes a first enlarging/reducing device to change a magnification ratio for the image, is provided upstream of the memory in a direction in which the digital image data is sent. A second enlarging/reducing device is produced to change a magnification ratio for the image, is provided downstream of the memory in the direction in which the digital image data is sent. The digital image data processed with the first enlarging/reducing device is stored in the memory and the digital image data read from the memory is again processed with the second enlarging/reducing device.
According to another embodiment of the present invention, the image forming apparatus includes an image quality enhancing device to process the digital image data to enhance a quality of the image according to the digital image data. The digital image data processed with the first enlarging/reducing device is stored in the memory after haying been processed with the image quality enhancing device, and the digital image data read from the memory is again processed with the second enlarging/reducing device.
According to still another embodiment of the present invention, the image forming apparatus includes a single enlarging/reducing device to change a magnification ratio for the image. A first switch device switches the digital image data to the enlarging/reducing device upstream of the memory in a direction in which the digital image data is sent, and a second switch device switches the digital image data read from the memory to the enlarging/reducing device to change a magnification ratio for the image.
According to still another embodiment of the present invention, a capacity of a FIFO memory used in the second enlarging/reducing device is smaller than a capacity of a FIFO memory used in the first enlarging/reducing device.